Embodiments of the present invention relate to test and measurement instrumentation, and more particularly to providing a trigger signal based upon a detection criteria.
Referring now to FIG. 1 (prior art), a real-time spectrum analyzer 10 is shown having an input processor 20 for receiving an input RF signal, or other signal of interest. The input processor 20 typically includes a lowpass filter 22 followed by a mixer 24 that converts the filtered input signal to an intermediate frequency (IF) signal using a local oscillator 26. The IF signal is passed through a bandpass filter 28 and then input to an analog-to-digital (A/D) converter 30 to provide a digital signal for further processing. The digital signal is input to a digital IF quadrature processor 31 to derive In-phase (I) and Quadrature-phase (Q) signals from the digital signal. The I and Q signals are input to a processor 32 for real-time processing for display on a monitor 34, which provides a representation of frequency vs. time. The I and Q signals are also input to an acquisition memory 36 and to a trigger generator 40. When the trigger generator 40 detects an event, a trigger is generated that causes acquisition memory 36 to hold data from before, after and/or during the trigger event for subsequent processing. Subsequent processing may be performed by the processor 32, or by additional processors (not shown). The subsequent processing may be used for real-time analysis or non-real-time analysis, such as post process analysis. The processor 32 may be implemented as a digital signal processor (DSP), an ASIC, an FPGA, or a general purpose processor, such as those used in general purpose, or personal computers.
In response to specified conditions that define a trigger event, the trigger generator outputs a trigger signal. A memory controller is said to capture I-Q data in response to the trigger signal. In some embodiments, the act of acquiring, or capturing, I-Q data is accomplished by holding data that is already stored in the memory, such that it will not be overwritten during the normal acquisition process. In other embodiments, the I-Q data may be transferred from a temporary memory, into a more permanent memory, or other storage medium for subsequent processing. Depending upon the desired action, I-Q data from some period prior to the trigger signal, some period subsequent to the trigger signal, or a combination thereof, may be captured, or stored, in response to the trigger signal. In some embodiments, the I-Q data corresponding to the signal that met the defined trigger event are also captured and stored.
The word trigger may generally refer interchangeably to the trigger circuit, the trigger signal, and in some instances the type of signal event that results in a trigger signal. Triggers are becoming more and more sophisticated as modem communications systems have become more complex. There is a growing desire to identify a variety of signals, or signal anomalies, that occur very infrequently in signals that may be present for very long periods of time. In these systems, while a problem may be known to exist, the source of the problem may be difficult to isolate or identify. This is especially true when the problem is intermittent. Long data records, on the order of hours or even day, may have to be examined to try to find the data corresponding to an event.
As signals become more complex, simple level triggers in the time domain, and even frequency mask triggers in the frequency domain are insufficient for providing the ability to trigger on more complex signals, or signal anomalies.